#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main() {
    long int n;
    static long int sum = 0;
    int i = 0;
    scanf("%d", &n);
    for (i = 0; i <= n; i++)
    {
        sum += i;
    }
    printf("%ld\n", sum);

    return 0;
}